An internal combustion engine is provided with a cooling device of a water cooling type to keep a cylinder head and a cylinder block at an appropriate temperature. The cooling device includes a cooling water circulating system that makes a cooling water circulate between a cooling water flow channel formed in the cylinder head and the cylinder block and a radiator. In Japanese Patent Laid-Open No. 2004-084526, a cooling device that controls the temperature of the cooling water according to the load condition of the internal combustion engine is described. According to the technique described in the patent literature, when the internal combustion engine is in a high load condition, the flow rate of the cooling water is increased to reduce the temperature of the cooling water in order to prevent occurrence of knocking.
In Japanese Patent Laid-Open No. 2013-133747 and Japanese Patent Laid-Open No. 2013-133746, cooling devices provided with two cooling water circulating systems are disclosed. One of the cooling water circulating systems is configured to make the cooling water circulate through a cooling water flow channel formed in the cylinder block and a cooling water flow channel formed in the vicinity of the exhaust port of the cylinder head. The other cooling water circulating system is configured to make the cooling water circulate through a cooling water flow channel formed in the vicinity of the intake port of the cylinder head.